A fuel injection valve provided in an internal combustion engine using gasoline and natural gas as fuel has a valve member received in a body having an injection port formed in a tip portion thereof in such a way as to be freely moved back and forth. The valve member is moved by a magnetic force of a solenoid provided in the body to thereby open the injection port, whereby the fuel is injected into the engine from the fuel injection valve.
In the solenoid, a supply of electricity is controlled by an electronic control unit (ECU) for comprehensively controlling the driving of the engine. Specifically, the supply of the electricity to the solenoid is controlled on the basis of a pulse signal that the ECU determines according to a driving state of the engine. That is, the ECU determines a pulse width and an output timing of the pulse signal according to the driving state of the engine to thereby control a timing when the fuel is injected from the fuel injection valve and an injection quantity. When the supply of the electricity to the solenoid is stopped, the valve member is moved by a resilient force of a spring member provided in the fuel injection valve and by a pressure of the fuel, whereby the injection port is closed by the valve member.
An electric resistance of the solenoid is changed according to a temperature of the solenoid (coil) and a temperature of the surroundings, so that also a time characteristic of current flowing through the solenoid is changed along with the temperatures. For example, when the temperature of the solenoid is increased, the electric resistance of the solenoid is increased, whereby a time that elapses before a magnetic force necessary for attracting the valve member is generated is elongated. As a result, a timing when the valve member opens the injection port is delayed from a timing when a pulse signal is inputted. When the supply of the electricity to the solenoid is finished, the valve member is moved by the resilient force of the spring member and the pressure of the fuel, thereby instantaneously closing the injection port. For this reason, a timing when the valve member closes the injection port is made roughly constant irrespective of the temperature of the solenoid. As a result, in the case where the temperature of the solenoid is increased, only a timing when the fuel is injected is delayed, which results in reducing the total quantity of the fuel to be supplied from the fuel injection valve.
Deterioration with time of the fuel injection valve causes a frictional force between the valve member and the body to increase in some cases. In this case, even if the solenoid is under the same temperature condition, the response of the valve member is delayed and hence the injection quantity of the fuel is made less than expected.
For example, in a patent document 1 is disclosed a technique of calculating an integral value of current flowing through a solenoid and comparing the calculated integral value with a standard value and making a feedback control to thereby correct a pulse width of a pulse signal. Specifically, the pulse width is changed according to the ratio of the integral value to the standard value, whereby the injection quantity of the fuel to be injected from the fuel injection valve is controlled in such a way as to be close to a standard quantity.
The method disclosed in the patent document 1 aims to correct the pulse width to thereby correct a deviation in the injection quantity. For this reason, it is not considered that an injection state such as an injection timing and a timing when the fuel injection valve is fully opened is deviated from a target injection state because of a change in the temperature of the solenoid and the deterioration with time of the solenoid. Hence, the fuel cannot be injected under an appropriate state according to the driving state of the engine and in particular the injection timing is delayed, whereby the torque and the emission (HC) of the engine are likely to be increased.